basically a good idea, but where would you draw the line? Many people are killed with cars (insured) and common kitchen knifes (not insured). There are precedences both for and against such a law.
At any rate it would make people more careful and hide their weapons better. That in itself would already be a big step forward.
A common kitchen knife is not deadly during its typical method of use. Cars are. Guns are. Insurance is about risk. The relative risk of injury or death in the presence of a gun (or a car) is orders of magnitude higher than in the presence of a kitchen knife.